Years of work went into it. They sent operatives to collect sand samples, planted fake evidence on a corpse, and even ran drills off the coast of england. The latter one almost gave it all away when some German submarines interrupted their practice.

IIRC training was done in Britain and Scotland using similar beaches/cliffs.

Training was being carried out all over the place for all sorts of things. The ski industry as it is today in the western US was (in my opinion) heavily influenced by Camp Hale being constructed in the Colorado mountains specifically to train thousands of soldiers to fight in the Alps, using donkeys, skiing, mountain climbing, etc.

After the war the ski areas were developed with former soldiers.